Tetherin is a HIV restriction factor that prevents release of enveloped viruses by mechanically linking the virus to the host cell membrane. This requires membrane insertion of tetherin's transmembrane domain and GPI anchor, as well as dimerization of tetherin's cytoplasmic ectodomains. The precise geometric arrangement of tetherin molecules and tetherin domains at sites of HIV-1 restriction are not well understood. Tetherin is recruited to discrete sites on the plasma membrane that correspond to regions of HIV-1 assembly and budding. The goal of this research proposal is to elucidate the three-dimensional (3D) structure of tethered HIV-1 virions and virus like particles (VLPs) and the tetherin microdomain. Specific Aim 1 - characterize the 3D structure of HIV-1 VLPs tethered to the plasma membrane of a mammalian cell by cryo-electron tomography (cryo-ET). Specific Aim 2 - characterize the 3D structure of the tetherin microdomain in HIV-1 permissive cells by correlative light electron microscopy (CLEM).